Hot water heaters are commonly used to supply hot water to household users. Generally, a hot water tank is connected to a pressurized water source. The water in the storage tank is heated by a source of energy, such as natural gas or electricity.
Hot water heaters operate with little or no maintenance. However, the mineral content of the water stored in a water heater can corrode and weaken the structure of the storage tank causing a leak or rupture. Excessive pressure in the storage tank caused by extreme water temperatures can also cause a rupture.
To minimize damage from water leakage, the prior art discloses several systems for isolating the water source from the storage tank when a rupture occurs. U.S. Pat No. 3,063,432 discloses a can beneath the water heater that collects water in the event of a leak. The collected water activates a circuit causing the water and fuel supplies to be cut off.
Other patents, such as U.S. Pat No. 2,724,401, disclose similar apparatus, but have not been economically practical. U.S. Pat No. 3,754,563 to Wayne S. Boals discloses an improved design describing a valve to control the flow between the water source and the storage tank. While the disclosed design works quite well, the apparatus includes numerous seals which could deteriorate under certain operating conditions. Further, the apparatus does not provide for a means of providing cold water to the water tank when the water achieves excessive temperatures and is discharged by a temperature-pressure relief valve.
Consequently, U.S. Pat No. 4,607,615 to Wayne S. Boals discloses an improved automatic control system for water heaters. The apparatus includes a diaphragm between a chamber measuring the pressure of the storage tank and a chamber measuring the pressure of the user system. The diaphragm reacts to differential pressure between the water source, the storage tank and the user system. When a leak or rupture occurs, the pressure from the storage tank drops to ambient pressure. The pressure from the user system is then higher than the pressure from the storage tank. This causes a stem to urge the diaphragm against a valve seat and prevents water from flowing from the cold water source into the storage tank. The Boals U.S. Pat. No. 4,607,615 does not provide a means to limit the extent the stem would move the diaphragm into the chamber measuring the pressure of storage tank. Nor does the Boals U.S. Pat. No. 4,607,615 patent provide a means to reset the diaphragm, and hence the control valve, once the leak or rupture is fixed.
The apparatus disclosed by Boals further prevents a water pressure loss occurring in the storage tank during a cooling cycle through a leak path in a valve seat. Due to manufacturing limitations, however, the leak path could not be made small enough to obtain the desired minimum flow rate into the storage tank under all conditions. The present invention is an improvement of the structure disclosed in the Boals U.S. Pat. No. 4,607,615.